The 2004 Aceh-Andaman Earthquake: Early clay dehydration controls shallow seismic rupture
The 2004 Aceh-Andaman Earthquake: Early clay dehydration controls shallow seismic rupture
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2004 年亚齐-安达曼地震：早期粘土脱水控制浅层地震破裂
DOI：
10.1002/ggge.20193
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发表时间：
2013
期刊：
影响因子：
--
通讯作者：
Geersen J
中科院分区：
文献类型：
--
作者：
Geersen J
浅板块边界断层的物理状态控制着俯冲带地震期间地震破裂的上倾程度，因此对此类事件的海啸危险产生一级影响。在2004年亚齐-安达曼9.2级地震中，地震破裂在增生棱柱体下方异常地向大海延伸，造成了灾难性的印度洋海啸。在这里，我们表明，形成一个强大的散装沉积物部分和高流体压力的预沉降，这可能使2004年破裂到达浅板边界，结果是在上部海洋基底和上覆沉积物的热控制成岩过程。沉积物剖面增厚到俯冲带向海方向>2 km至160 km，增加了沉积物基底界面的温度，并触发矿物转化和脱水（例如，蒙皂石-伊利石）。释放的流体迁移到一个层，可能主机高孔隙度和渗透性，这是唯一的2004年破裂区，在那里他们产生一个明显的超压predécollement。粘土矿物转化进一步支持沉积物的半石化、硬化过程，并与压实脱水相结合，所有这些都被厚沉积物部分放大，共同加强了大块沉积物。在更远的南部，2005年苏门答腊地震没有包括类似的浅层破裂，海洋板块上的沉积物厚度明显较小。因此，类似的成岩作用在俯冲带发生得更晚、更深。因此，我们认为，2004年地震期间的浅源地震破裂主要是由海洋板块沉积物的厚度和成分控制的。
The physical state of the shallow plate‐boundary fault governs the updip extent of seismic rupture during powerful subduction zone earthquakes and thus on a first order impacts on the tsunamigenic hazard of such events. During the 2004 Mw 9.2 Aceh‐Andaman Earthquake seismic rupture extended unusually far seaward below the accretionary prism causing the disastrous Indian Ocean Tsunami. Here we show that the formation of a strong bulk sediment section and a high fluid‐pressured predécollement, that likely enabled the 2004 rupture to reach the shallow plate‐boundary, result from thermally controlled diagenetic processes in the upper oceanic basement and overlying sediments. Thickening of the sediment section to >2 km ∼160 km seaward of the subduction zone increases temperatures at the sediment basement interface and triggers mineral transformation and dehydration (e.g., smectite‐illite) prior to subduction. The liberated fluids migrate into a layer that likely host high porosity and permeability and that is unique to the 2004 rupture area where they generate a distinct overpressured predécollement. Clay mineral transformation further supports processes of semilithification, induration of sediments, and coupled with compaction dewatering all amplified by the thick sediment section together strengthens the bulk sediments. Farther south, where the 2005 Sumatra Earthquake did not include similar shallow rupture, sediment thickness on the oceanic plate is significantly smaller. Therefore, similar diagenetic processes occur later and deeper in the subduction zone. Hence, we propose that shallow seismic rupture during the 2004 earthquake is primarily controlled by the thickness and composition of oceanic plate sediments.